1. Field of the Invention
This invention relates generally to an extrusion die and a method of making the same, and more specifically to an extrusion die having on the front surface thereof a bearing opening of the shape of a given section, and a draft formed over a length from the bearing opening toward the rear surface of the die wherein all or part of the bearing surface and the draft constituting the inner circumferential surface of the bearing opening are formed by means of the wire- gutting discharge machining equipment, and a method of making the same.
2. Description of the Prior Art
An extrusion die as illustrated in FIGS. 1 (A) through (C) is known as a conventional type of extrusion die for extruding aluminum extrusions. FIG. 1 (A) is a plan view, FIG. 1 (B) is a sectional side elevation taken along line A-A' in FIG. 1 (A), and FIG. 1 (C) is a bottom plan view of the conventional type of extrusion die, respectively. In the figures, reference numeral 1 refers to an entrance portion; 2 to a bearing opening; 3 to a draft; and 4 to a shouldered portion of the draft 3, respectively.
In general, when manufacturing an extrusion, like an aluminum sash, by forcing material through an extrusion die, an aluminum slug fed into the entrance portion 1 is forced toward the bearing opening 2 by means of an extrusion press (not shown), formed into a given shape by the bearing opening 2, and forced out of the draft 3 in the form of an extrusion. Consequently, to manufacture an extrusion with high precision, it is necessary to keep the rate of aluminum slug passing through the bearing opening 2 uniform. To achieve this, it has been conceived that the bearing length (1 as shown by arrows in FIG. 1 (B)) of the bearing opening 2 is adjusted in accordance with the shape of the bearing opening 2, as will be described later, referring to FIGS. 2 and 3. In the following, the bearing length 1 will be described.
FIGS. 2 (A), (B) and (C) are crosssectional views taken along lines A-A', B-B' and C-C', respectively in FIG. 1, and FIG. 3 is a development of the bearing surface. Reference numerals 2 through 4 throughout the figures correspond with like numerals in FIG. 1, and 5 refers to a bearing surface and 6 to a draft tapered surface, respectively.
As noted earlier, the bearing length 1 (as shown in FIG. 1 (B)) in the bearing opening 2 is predetermined in accordance with the shape of the bearing opening 2. That is, the bearing length, 1.sub.c is made larger, as shown in FIG. 2 (C), in a bearing opening portion having a larger width and the adjacent portions thereof, de is shown by arrows in FIG. 1 (C), while the bearing length, 1.sub.b is made smaller, as shown in FIG. 2 (B), in bearing opening portions, bc and fg having a smaller width, as shown by arrows in FIG. 1 (C). Furthermore, the bearing length, 1.sub.a is made further smaller, as shown in FIG. 2 (A), in a bearing opening end portion, ha as shown by arrows in FIG. 1 (C), which has the same width as the adjacent portions thereof but involves retarded metal flow. The bearing surface thus formed assumes a shape shows in FIG. 3 in a developed form. Arrows a through h in FIG. 3 correspond to the arrows a through h in FIG. 1 (C).
The bearing surface 5 of the bearing opening 2 in the conventional type of extrusion die described above is machined by the wire-cutting discharge machining equipment, while the draft shouldered portion 4 and the draft tapered surface 6 are machined by an ordinary discharge machining equipment, milling machine or other type of machine tool. The machining of the draft shouldered portion 4 is required because it is difficult to form with high precision the aforementioned bearing lengths 1.sub.a, 1.sub.b and 1.sub.c, and the portions between ab, cd, ef and gh as shown in FIG. 3 merely by machining the bearing surface 5 and the draft tapered surface 6. As a result, the following problems are encountered in manufacturing an extrusion die of the conventionad type.
(i) Complex die manufacturing processes are needed, and the workpiece has to be positioned precisely in each manufacturing process. PA1 (ii) As described above, the machining of the draft 3 with ordinary discharge machining equipment requires the manufacture of several types of machining electrodes, all of which have to be machined with high precision. The machining of the draft 3 with a milling machine also requires sophisticated machining techniques. PA1 (iii) The high-prescision machining of an extrusion die of thc conventional type with the abovementioned machining methods is difficult because of electrode consumption in discharge machining, and because of cutter wobbling in milling.
Due to the aforementioned problems, the conventional type of extrusion die involves a large number of manhours and high manufacturing costs. Furthermore, provision of the draft shouldered portion 4 tends to decrease mechanical strength in the portions close to the bearing opening 2, leading to deformation and cracks in the thin-walled portions around the bearing opening 2.